Teeth are polished with compositions comprising one or more mild abrasives as part of routine dental prophylaxis by professional dental worker. Polishing is intended to increase the smoothness of the tooth surface thereby optimizing the tooth surface and minimizing surface defects, remove surface stains (extrinsic stains), increase resistance against surface staining, and remove plaque and pellicle, thereby preventing or reducing the risk of gum disease. Tooth abrasion, however, can eventually wear away enamel, dentin, and cementum over time. In addition, people vary in their propensity to develop extrinsic stains and plaque. Furthermore, susceptibility to abrasion is increased in the presence of erosion, such as that caused by acid, of the surface of a tooth (Hunter et al., 2002, Int. Den. J. 52: 399-405). Acid selectively removes some components of tooth, thereby eroding the tooth surface by increasing surface area and surface roughness. Peroxide is known to have a similar effect. Thus, careful selection of polishing materials and technique is required to balance stain removal and tooth surface integrity for each patient.
There are three major categories of abrasives currently used for polishing teeth: phosphates, including orthophosphates, polymetaphosphates, and pyrophosphates; carbonates; and silicas. Aluminum oxide is also used as an abrasive. The abrasives are found in both toothpaste formulas, as well as prophylaxis pastes. Prophylaxis pastes are products that are professionally used by the dentist and/or the dental hygienist to polish teeth. Other abrasives include resinous abrasive materials, such as particulate condensation products of urea and formaldehyde, and those disclosed U.S. Pat. No. 3,070,510.
Professional polishing involves mechanical polishing tips (e.g, a rubber cup or a brush) driven by a slow-speed device, and/or air polishing. The mechanical polishing tips may be used alone or with prophylaxis pastes. Air polishing uses air, sodium bicarbonate and a water jet to remove stains and polish the teeth. In addition to the risk of undesirable tooth abrasion, some other problems with current professional polishing techniques include splattering of the prophylaxis paste, discomfort arising from frictional heat of the polishing tip, sensitivity of eroded tooth surfaces, and sensitivity of soft tissues, including gums, tongue and lips, to air polishing. Additionally, air polishing is not advisable for patients with exposed cementum or dentin.
Chlorine dioxide (ClO2) is well known as a disinfectant as well as a strong oxidizing agent. The bactericidal, algaecidal, fungicidal, bleaching, and deodorizing properties of chlorine dioxide are also well known.
Chlorine dioxide (ClO2) is a neutral compound of chlorine in the +IV oxidation state. It disinfects by oxidation. However, it does not chlorinate. It is a relatively small, volatile, and highly energetic molecule, and a free radical even while in dilute aqueous solutions. Chlorine dioxide functions as a highly selective oxidant due to its one-electron transfer mechanism where it is reduced to chlorite (ClO2−). The pKa for the chlorite ion/chlorous acid equilibrium is extremely low at pH 1.8. This is remarkably different from the hypochlorous acid/hypochlorite base ion pair equilibrium found near neutrality, and indicates that the chlorite ion will exist as the dominant species in drinking water.
One of the most important physical properties of chlorine dioxide is its high solubility in water, particularly in chilled water. In contrast to the hydrolysis of chlorine gas in water, chlorine dioxide in water does not hydrolyze to any appreciable extent but remains in solution as a dissolved gas.
The traditional method for preparing chlorine dioxide involves reacting sodium chlorite with gaseous chlorine (Cl2(g)), hypochlorous acid (HOCl), or hydrochloric acid (HCl). The reactions are:2NaClO2+Cl2(g)=2ClO2(g)+2NaCl  [1a]2NaClO2+HOCl=2ClO2(g)+NaCl+NaOH  [1b]5NaClO2+4HCl=4ClO2(g)+5NaCl+2H2O  [1c]Reactions [1a] and [1b] proceed at much greater rates in acidic medium, so substantially all traditional chlorine dioxide generation chemistry results in an acidic product solution having a pH below 3.5. Also, because the kinetics of chlorine dioxide formation are high order in chlorite anion concentration, chlorine dioxide generation is generally done at high concentration (>1000 ppm), which must be diluted to the use concentration for application.
Chlorine dioxide may also be prepared from chlorate anion by either acidification or a combination of acidification and reduction. Examples of such reactions include:2NaClO3+4HCl→2ClO2+Cl2+2H2O+2NaCl  [2a]2HClO3+H2C2O4→2ClO2+2CO2+2H2O  [2b]2NaClO3+H2SO4+SO2→2ClO2+2NaHSO4  [2c]At ambient conditions, all reactions require strongly acidic conditions; most commonly in the range of 7-9 N. Heating of the reagents to higher temperature and continuous removal of chlorine dioxide from the product solution can reduce the acidity needed to less than 1 N.
A method of preparing chlorine dioxide in situ uses a solution referred to as “stabilized chlorine dioxide.” Stabilized chlorine dioxide solutions contain little or no chlorine dioxide, but rather, consist substantially of sodium chlorite at neutral or slightly alkaline pH. Addition of an acid to the sodium chlorite solution activates the sodium chlorite, and chlorine dioxide is generated in situ in the solution. The resulting solution is acidic. Typically, the extent of sodium chlorite conversion to chlorine dioxide is low and a substantial quantity of sodium chlorite remains in the solution.
U.S. Pat. No. 6,582,682 discloses an oral care composition comprising “stabilized chlorine dioxide” that, upon exposure to the mildly acidic pH in the oral cavity, produces chlorine dioxide.
U.S. Pat. No. 6,479,037 discloses preparing a chlorine dioxide composition for tooth whitening, wherein the composition is prepared by combining a chlorine dioxide precursor (CDP) portion with an acidulant (ACD) portion. The CDP portion is a solution of metal chlorite at a pH greater than 7. The ACD is acidic, for example having a pH of 3.0 to 4.5. The CDP is applied to the tooth surface. The ACD is then applied over the CDP to activate the metal chlorite and produce chlorine dioxide. The pH at the contact interface can be less than 6 and, in the another range of about 3.0 to 4.5. Thus, the resulting chlorine dioxide composition on the tooth surface is acidic. Additionally, this method exposes the oral mucosa to possible contact with a strongly highly acidic reagent (ACD).
U.S. Pat. No. 6,432,387 discloses a tooth polishing agent that generates negative ions in the mouth, effectively cleaning the teeth with a reduced amount of abrasives and aggressive brushing.
Yet a need remains in the art for tooth polishing compositions and methods with reduced side effects.